Mold blocks for forming coupler collar integral with pipe

ABSTRACT

A pair of cooperating mold blocks for forming an enlarged coupler collar on a corrugated plastic pipe being molded therein. The mold blocks have a mold surface including a corrugated portion defined by a series of alternating ribs and valleys and a non-corrugated portion defined by a relatively smooth semicylindrical wall having a diameter greater than the diameter of the valleys in the corrugated portion and adapted for forming the relatively enlarged coupler collar. The semicylindrical wall includes a plurality of arcuately spaced projections adapted for forming inwardly projecting latching members on the wall of the plastic pipe being molded thereagainst.

United States Patent Maroschak MOLD BLOCKS FOR FORMING COUPLER COLLARINTEGRAL WITH PIPE [76] Inventor: Ernest J. Maroschak, Box 878,

Roseboro, NC. 28382 [22] Filed: Feb. 20, 1973 21 Appl. No.: 333,996

Related US. Application Data [63] Continuation-impart of Ser. No.271,225, July 13,

[52] US. Cl 425/326, 264/151, 425/DIG. 206 [51] Int. Cl. B29c 17/00Field of Search... 249/160, 161, 162, 164, 1.73, 249/163; 425/396, 392,336, 369, 326 B, 326 B], 387 B, 388, 335, DIG. 206; 264/209,

[451 Feb. 19, 1974 Primary ExaminerJ. Spencer Overholser AssistantExaminer.lohn S. Brown Attorney, Agent, or Firm-Parrott, Bell, Seltzer,Park & Gibson [57] ABSTRACT A pair of cooperating mold blocks forforming an enlarged coupler collar on a corrugated plastic pipe beingmolded therein. The mold blocks have a mold surface including acorrugated portion defined by a series of alternating ribs and valleysand a noncorrugated portion defined by a relatively smoothsemicylindrical wall having a diameter greater than the diameter of thevalleys in the corrugated portion and adapted for forming the relativelyenlarged coupler collar. The semicylindrical wall includes a pluralityof arcuately spaced projections adapted for forming inwardly projectinglatching members on the wall of the plastic pipe being moldedthereagainst.

9 Claims, 5 Drawing Figures MOLD BLOCKS FOR FORMING COUPLER COLLARINTEGRAL WITH PIPE This application is a continuation-in-part of mycopending application Ser. No. 271,225 filed July 13, 1972, and entitledMETHOD AND APPARATUS FOR MAKING CORRUGATED PLASTIC PIPE WITH INTEGRALCOUPLER COLLARS.

It has previously been the practice to produce corrugated plastic pipeswith corrugations over the entire length thereof and to interconnectadjoining pipes with separate sleeve-like coupler elements. In myaforementioned copending application a method and apparatus forproducing an improved corrugated plastic pipe is disclosed wherein thepipe is provided with a coupler collar integrally formed at one endthereof to facilitate interconnection of adjoining lengths of the pipe.

It is an object of this invention to provide a pair of mold blocksadapted for forming a relatively enlarged coupler integral with acorrugated plastic pipe being molded therein.

It is a further and more specific object of this invention to provide apair of cooperating mold blocks adapted for use in a continuous blowmolding machine employing an endless series of forwardly movingcooperating pairs of mold blocks, wherein the pair of mold blocks has acorresponding pair of mold surfaces adapted for forming a relativelyenlarged noncorrugated coupler collar integral with a corrugated plasticpipe.

Some of the objects of the invention having been stated, other objectswill appear as the description proceeds when taken in connection withthe accompanying drawings, in which FIG. 1 is a perspective view of anextruder and a blow molding machine adapted to use a pair of mold blocksaccording to the present invention;

FIG. 2 is a schematic side view illustrating the drive means for movingthe mold blocks of the present invention in a blow molding machine;

FIG. 3 is a perspective view of a pair of mold blocks according to thepresent invention;

FIG. 4 is a cross sectional view of the mold surfaces of a pair of moldblocks looking in the direction of arrows 4-4 in FIG. 2 and FIG. 5 is aperspective view of a mold block according to the present inventionshowing the underside thereof.

Referring now more particularly to the drawings and first to FIG. 1,there is shown a conventional apparatus for molding plastic pipeincluding an extruder l0 and a blow molding machine 20. The extruder isarranged to extrude a tube of softened thermoplastic material into anelongate blow molding zone 21 formed by a plurality of cooperating pairsof mold blocks arranged in end-to-end relation in two opposing endlessseries 22, 23. The mold blocks in each endless series move forwardlytogether along the substantially straight blow molding zone 21 incooperating pairs with each cooperating pair of mold blocks forming amold cavity and with the cavities of all the mold blocks in the blowmolding zone together forming an elongate composite mold cavity of thedesired internal configuration. Upon reaching the downstream end of theblow molding zone, the cooperating pairs of mold blocks separate andreturn upstream along their respective endless paths to the beginning ofthe blow molding zone. As is conventional, the extruder is provided withsuitable pressure means 11 for introducing compressed air or other fluidinto the tube being extruded to expand and mold the tube against thewall of the composite mold cavity in the blow molding zone.

Blow molding machine 20 is provided with suitable drive means 24 formoving the mold blocks around their respective endless paths. As shownin FIG. 2, the drive means 24 preferably includes a toothed gear 25driven by an electric motor or other suitable means, not shown, andwhich meshingly engages a corresponding toothed area on the underside ofthe mold blocks. As illustrated in FIG. 5, each mold block 30 preferablyhas a series of parallel gear teeth 31 similar to a rack gear formed onthe underside of the mold block and extend- I ing along the axialdimension of the mold block. The gear teeth 31 on both of the moldblocks in the pair are preferably engaged simultaneously by toothed gear25 so that the pair of cooperating mold blocks are moved simultaneouslyin the blow molding zone.

As is known, continuously corrugated plastic pipe may be produced on ablow molding machine of the type previously described by providing eachmold block in the machine with a mold surface having a continuous seriesof corrugations thereon. As disclosed in my aforementioned copendingapplication, an improved pipe having a relatively enlarged couplercollar integrally formed therewith may be molded in such a blow moldingmachine by providing most of the cooperating pairs of mold blocks in theblow molding machine with corrugations of annular ribs and valleysthroughout the mold cavity while providing certain other cooperatingpairs of mold blocks with a mold cavity in accordance with the presentinvention wherein the mold cavity includes a generally smooth relativelyenlarged cylindrical portion and a corrugated portion with corrugationsof alternating annular ribs and annular valleys.

FIG. 3 illustrates a pair of mold blocks 30 in accordance with thepresent invention. The mold blocks are preferably machined from steelstock and are subsequently hardened as is conventional. They are formedin cooperating pairs and include substantially planar exterior surfaces32 and corresponding concave mold surfaces 33 which cooperate to definea generally cylindrical mold cavity extending through the center of theassembled pair of cooperating mold blocks, from one end thereof to theopposite end. As illustrated, the

mold blocks have a length of about 4.17 inches along' the axialdimension of the blocks and a height of about 5.5 inches. The width of acooperating pair of the blocks is also about 5.5 inches. The upper andlower surfaces of the blocks are provided with rounded shoulder portions34, 35 (FIGS. 3 and 5) which extend generally axially of the mold blocksand which aid the mold blocks in turning the relatively small radius atopposite reaches or ends of each respective endless series. To furtherfacilitate turning the relatively small radius, the vertical edges 36along the back side of each mold block are beveled or rounded slightlyas shown in FIG. 3.

As seen from FIG. 3, the mold surface 33 of each of the mold blocks hasa portion thereof including a series of semicircular transversealternating ribs 37 and valleys 38 which form corrugations on the moldsurface. These ribs and valleys have generally flat peripheral surfacesalong the axial dimension of the mold surface. Stated otherwise, each ofthe ribs and valleys are of substantially uniform diameter. Theremaining portion of the mold surface is defined by a relatively smoothsemicylindrical wall 39 of a diameter substantially greater than thediameter of the valleys in the corrugated portion of the mold surface.When the corresponding concave mold surfaces of the pair of mold blocksare positioned together in assembled relationship, the transversealternating ribs and valleys of each mold surface cooperate to definecontinuous uninterrupted annular corrugations in one portion of the moldcavity, while the relatively smooth semicylindrical walls cooperate todefine a relatively smooth cylindrical portion of the mold cavity havinga diameter greater than that in the corrugated portion. Preferably thevalleys in the corrugated portion have a diameter of about 4 incheswhile the relatively smooth-walled portion has a diameter of about 4%inches. The ribs in the corrugated portion of the mold cavity have adiameter of about 4 inches.

As illustrated in FIG. 4, the corrugated portion of the mold surfaceincludes four ribs and three valleys with a half valley portion at oneend of the mold block. The corrugated portion extends from one end ofthe mold block and over at least half the axial length thereof. The ribsand valleys on the mold surface are generally flat, as previously noted,with the valleys being somewhat wider than the ribs. The ribs includegenerally flat side wall portions 41 which are tapered or inclined at anacute angle to a plane normal to the axis of the mold cavity.

The relatively enlarged smooth-walled portion of the mold surfaceextends from adjacent the innermost rib on the mold surface to the endof the mold block opposite the corrugated portion. The axial length ofthis smooth-walled portion corresponds to at least twice the distancebetween corresponding points on adjacent valleys in the corrugatedportion, so that when a coupler collar is molded in the smooth-walledportion, it will accommodate a length of pipe including at least tworibs of the size corresponding to the valleys in the corrugated portionof the mold block. As shown, this length corresponds to at least about1.39 inches and preferably about 1.59 inches.

Positioned on the relatively smooth-walled portion of each mold surfaceare a series of relatively small arcuately spaced, radially inwardlydirected projections 42 which are adapted for forming correspondinglyshaped inward projections on the coupler collar being molded against thesmooth-walled portion of the mold surface. The projections on thecoupler collar serve as latch members for engaging and releasablyretaining the end of a corrugated pipe in the coupler collar. As shownin FIGS. 3 and 4, the projections are spaced axially inwardly from theend of the mold block a substantially equal distance and are arcuatelyspaced apart around the inner circumference of the mold surface bysubstantially equal distances. Preferably, two projections are providedon each mold surface and are positioned 90 apart so as to cooperate inopposing pairs with the projections on the corresponding mold block ofthe pair. Although not illustrated, in some instances it may bedesirable to provide an additional row of spaced projections inwardly ofthe aforementioned illustrated series of projections to provideadditional engagement with the corrugations at the end of a corrugatedpipe. The projections are provided on the mold surface preferably bymeans of separate inserts of the desired shape which are secured to thesmooth-walled portion of the mold surface by an adhesive, cold solder,or other suitable means. The projections may however. if desired, beformed integral with the mold surface.

Preferably, and as illustrated in FIGS. 3 and 4, the projections 42 havea prisimoidal or wedge-like shape and include two major opposingsurfaces 43, 44 with one surface 43 being angularly oriented andconverging inwardly from the end of the mold block and with the secondopposing surface 44 lying in a plane substantially perpendicular to theaxis of the mold cavity. The wedge-shaped projections also include endwalls 45 at opposite ends thereof. The wedge-shaped projectionsdesirably have a length of about three-fourths inch and a height ofabout one-eighth inch, which height is less than the depth of thevalleys in the corrugated portion of the mold blocks.

From the foregoing, it can be seen that a pair of cooperating moldblocks has been provided which is adapted for forming an enlargednon-corrugated coupler collar as an integral part of a corrugatedplastic pipe. While the mold blocks of the present invention have beendescribed with reference to a particular blow molding machine, it shouldbe apparent that the mold blocks of the present invention may be used inassocia tion with molding apparatus other than the particular blowmolding machine described herein.

In the drawing and specification, there has been set forth a preferredembodiment of the invention and although specific terms are employed,they are used in a generic and descriptive sense only and not forpurposes of limitation.

That which is claimed is:

1. A pair of mold blocks adapted for forming an enlarged coupler collaron a corrugated plastic pipe being molded therein, said pair of moldblocks having corresponding concave mold surfaces which cooperate todefine a generally cylindrical mold cavity extending from one end of thecooperating pair of mold blocks to the opposite end, each mold blockhaving a series of semicircular transverse alternating ribs and valleysforming a corrugated portion on the concave mold surface and extendingfrom one end of the mold block and over a predetermined axial length ofthe mold surface, the ribs and valleys of each of the mold blocks cooperating to form uninterrupted annular ribs and annular valleys in aportion of the mold cavity, a semicylindrical wall forming the remainingportion of the concave mold surface and extending from adjacent saidcorrugated portion to the opposite end of the mold block and having adiameter substantially greater than that of the valleys in thecorrugated portion of the mold surface, the semicylindrical wall of eachof the mold blocks cooperating to form a relatively enlarged generallycylindrical portion of the mold cavity, a plurality of arcuately spacedrelatively short projections extending radially inwardly from saidsemicylindrical wall and spaced axially inwardly a short distance fromsaid opposite end of the pair of cooperating mold blocks.

2. A pair of mold blocks according to claim 1 wherein said series ofalternating ribs and valleys extends over at least half the axial lengthof said mold surface.

3. A pair of mold blocks according to claim 1 wherein the innerperipheries of the ribs and valleys are substantially flat in the axialdirection and wherein the side walls of the ribs are substantially flatand form an acute angle with a plane normal to the axis of the moldcavity.

4. A pair of mold blocks according to claim 1 wherein saidsemicylindrical wall has an axial length of at least twice the distancebetween corresponding points on adjacent valleys in the corrugatedportion of said mold surface.

5. A pair of mold blocks according to claim 1 wherein the valleys in thecorrugated portion of said mold surface have a diameter of about 4%inches and wherein the semicylindrical wall has a diameter of about 4%inches.

6. A pair of mold blocks according to claim 1 wherein each mold blockhas an axial length of about 4.17 inches and wherein saidsemicylindrical wall has an axial length of at least about 1.39 inches.

7. A pair of mold blocks according to claim 1 wherein said projectionsare wedge-shaped and have one opposing surface thereof lying in a planewhich is angularly oriented with respect to the axis of said mold cavityand converging inwardly from said opposite end of the mold blocks andhave a second opposing surface lying in a common plane substantiallyperpendicular to the axis of said mold cavity.

8. A pair of mold blocks for use in a continuous blow molding machineemploying two endless series of abutting forwardly moving cooperatingpairs of mold blocks, said pair of mold blocks having correspondingconcave mold surfaces which cooperate to define a generally cylindricalmold cavity extending from one end of the pair of mold blocks to theopposite end and being adapted for forming an enlarged coupler collar ona corrugated plastic pipe being molded therein, each mold block having aseries of semicircular transverse alternating ribs and valleys forming acorrugated portion on the concave mold surface and extending from oneend of the mold block and over at least about half the axial length ofthe mold surface, the ribs and valleys of each of the mold blockscooperating to form uninterrupted annular ribs and annular valleys in aportion of the mold cavity, a semicylindrical wall forming the remainingportion of the concave mold surface and extending from adjacent saidcorrugated portion to the opposite end of the mold block and over anaxial length of at least about twice the distance between correspondingpoints on adjacent valleys in the corrugated portion of the moldsurface, said semicylindrical wall having a diameter substantiallygreater than that of the valleys in the corrugated portion of the moldsurface, the semicylindrical wall of each of the mold blocks cooperatingto form a relatively enlarged generally cylindrical portion of the moldcavity, a plurality of arcuately spaced projections positioned on thesemicylindrical wall and extending radially inwardly therefrom, saidprojections being located on said semicylindrical wall so as to bearcuately spaced substantially equally apart around the interior of thecylindrical portion of the mold cavity and axially spaced substantiallyequally inwardly from said opposite end of the mold blocks, and gearmeans integral with an exterior surface of the mold block for engagingwith drive means in a blow molding machine to move the pair of moldblocks simultaneously in the blow molding machine.

9. A pair of mold blocks according to claim 8 wherein said projectionsare defined by separate wedge-shaped segments secured to saidsemicylindrical wall and having one surface thereof lying in a planewhich is angularly oriented with respect to the axis of said mold cavityand converging inwardly from said opposite end of the mold blocks andhaving a second surface thereof lying in a plane substantiallyperpendicular to the axis of said mold cavity.

1. A pair of mold blocks adapted for forming an enlarged coupler collaron a corrugated plastic pipe being molded therein, said pair of moldblocks having corresponding concave mold surfaces which cooperate todefine a generally cylindrical mold cavity extending from one end of thecooperating pair of mold blocks to the opposite end, each mold blockhaving a series of semicircular transverse alternating ribs and valleysforming a corrugated portion on the concave mold surface and extendingfrom one end of the mold block and over a predetermined axial length ofthe mold surface, the ribs and valleys of each of the mold blockscooperating to form uninterrupted annular ribs and annular valleys in aportion of the mold cavity, a semicylindrical wall forming the remainingportion of the concave mold surface and extending from adjacent saidcorrugated portion to the opposite end of the mold block and having adiameter substantially greater than that of the valleys in thecorrugated portion of the mold surface, the semicylindrical wall of eachof the mold blocks cooperating to form a relatively enlarged generallycylindrical portion of the mold cavity, a plurality of arcuately spacedrelatively short projections extending radially inwardly from saidsemicylindrical wall and spaced axially inwardly a short distance fromsaid opposite end of the pair of cooperating mold blocks.
 2. A pair ofmold blocks according to claim 1 wherein said series of alternating ribsand valleys extends over at least half the axial length of said moldsurface.
 3. A pair of mold blocks according to claim 1 wherein the innerperipheries of the ribs and valleys are substantially flat in the axialdirection and wherein the side walls of the ribs are substantially flatand form an acute angle with a plane normal to the axis of the moldcavity.
 4. A pair of mold blocks according to claim 1 wherein saidsemicylindrical wall has an axial length of at least twice the distancebetween corresponding points on adjacent valleys in the corrugatedportion of said mold surface.
 5. A pair of mold blocks according toclaim 1 wherein the valleys in the corrugated portion of said moldsurface have a diameter of about 4 1/2 inches and wherein thesemicylindrical wall has a diameter of about 4 5/8 inches.
 6. A pair ofmold blocks according to claim 1 wherein each mold block has an axiallength of about 4.17 inches and wherein said semicylindrical wall has anaxial length of at least about 1.39 inches.
 7. A pair of mold blocksaccording to claim 1 wherein said projections are wedge-shaped and havEone opposing surface thereof lying in a plane which is angularlyoriented with respect to the axis of said mold cavity and converginginwardly from said opposite end of the mold blocks and have a secondopposing surface lying in a common plane substantially perpendicular tothe axis of said mold cavity.
 8. A pair of mold blocks for use in acontinuous blow molding machine employing two endless series of abuttingforwardly moving cooperating pairs of mold blocks, said pair of moldblocks having corresponding concave mold surfaces which cooperate todefine a generally cylindrical mold cavity extending from one end of thepair of mold blocks to the opposite end and being adapted for forming anenlarged coupler collar on a corrugated plastic pipe being moldedtherein, each mold block having a series of semicircular transversealternating ribs and valleys forming a corrugated portion on the concavemold surface and extending from one end of the mold block and over atleast about half the axial length of the mold surface, the ribs andvalleys of each of the mold blocks cooperating to form uninterruptedannular ribs and annular valleys in a portion of the mold cavity, asemicylindrical wall forming the remaining portion of the concave moldsurface and extending from adjacent said corrugated portion to theopposite end of the mold block and over an axial length of at leastabout twice the distance between corresponding points on adjacentvalleys in the corrugated portion of the mold surface, saidsemicylindrical wall having a diameter substantially greater than thatof the valleys in the corrugated portion of the mold surface, thesemicylindrical wall of each of the mold blocks cooperating to form arelatively enlarged generally cylindrical portion of the mold cavity, aplurality of arcuately spaced projections positioned on thesemicylindrical wall and extending radially inwardly therefrom, saidprojections being located on said semicylindrical wall so as to bearcuately spaced substantially equally apart around the interior of thecylindrical portion of the mold cavity and axially spaced substantiallyequally inwardly from said opposite end of the mold blocks, and gearmeans integral with an exterior surface of the mold block for engagingwith drive means in a blow molding machine to move the pair of moldblocks simultaneously in the blow molding machine.
 9. A pair of moldblocks according to claim 8 wherein said projections are defined byseparate wedge-shaped segments secured to said semicylindrical wall andhaving one surface thereof lying in a plane which is angularly orientedwith respect to the axis of said mold cavity and converging inwardlyfrom said opposite end of the mold blocks and having a second surfacethereof lying in a plane substantially perpendicular to the axis of saidmold cavity.